Download one session's full event log as a file.

The response is a single JSON object — session metadata plus every event in the session, oldest first, each with its full payload — served as an attachment (Content-Disposition: attachment; filename="session-<id>.json"). These are the exact bytes an evaluator receives for the session, so a downloaded file can be replayed through an evaluator unchanged.

There is no pagination and no size cap: a long session downloads in full, in one response. session_id is scoped to your organization — a session belonging to another organization reads as unknown and returns 404.